Intra block copy prediction restrictions in video coding

ABSTRACT

An example method includes determining, for each respective coding block of a plurality of coding blocks of a current coding tree unit (CTU) of video data in a current picture of video data, a respective search area of a plurality of respective search areas, wherein at least one of the plurality of search areas includes samples of the current picture located outside of the current CTU, and wherein at least one of the plurality of search areas does not include samples of the current picture located outside of the current CTU; selecting, for each respective coding block and from within the respective search area for the respective coding block, a respective predictor block of a plurality of predictor blocks; and reconstructing samples of each respective coding block based on samples included in a corresponding predictor block in the plurality of predictor blocks.

This application is a continuation of U.S. patent application Ser. No.16/663,033, filed 24 Oct. 2019, which claims the benefit of U.S.Provisional Patent Application No. 62/751,585, filed 27 Oct. 2018, theentire content of each application is incorporated herein by reference.

TECHNICAL FIELD

This disclosure relates to video encoding and video decoding.

BACKGROUND

Digital video capabilities can be incorporated into a wide range ofdevices, including digital televisions, digital direct broadcastsystems, wireless broadcast systems, personal digital assistants (PDAs),laptop or desktop computers, tablet computers, e-book readers, digitalcameras, digital recording devices, digital media players, video gamingdevices, video game consoles, cellular or satellite radio telephones,so-called “smart phones,” video teleconferencing devices, videostreaming devices, and the like. Digital video devices implement videocoding techniques, such as those described in the standards defined byMPEG-2, MPEG-4, ITU-T H.263, ITU-T H.264/MPEG-4, Part 10, Advanced VideoCoding (AVC), the High Efficiency Video Coding (HEVC) standard, ITU-TH.265/High Efficiency Video Coding (HEVC), and extensions of suchstandards. The video devices may transmit, receive, encode, decode,and/or store digital video information more efficiently by implementingsuch video coding techniques.

Video coding techniques include spatial (intra-picture) predictionand/or temporal (inter-picture) prediction to reduce or removeredundancy inherent in video sequences. For block-based video coding, avideo slice (e.g., a video picture or a portion of a video picture) maybe partitioned into video blocks, which may also be referred to ascoding tree units (CTUs), coding units (CUs) and/or coding nodes. Videoblocks in an intra-coded (I) slice of a picture are encoded usingspatial prediction with respect to reference samples in neighboringblocks in the same picture. Video blocks in an inter-coded (P or B)slice of a picture may use spatial prediction with respect to referencesamples in neighboring blocks in the same picture or temporal predictionwith respect to reference samples in other reference pictures. Picturesmay be referred to as frames, and reference pictures may be referred toas reference frames.

SUMMARY

In general, this disclosure describes techniques for improving thecoding efficiency and/or the memory requirements of coding video datausing current picture reference (CPR)/intra block copy (IBC) mode. Forinstance, a video coder (e.g., video encoder or video decoder) mayutilize a different search area for each coding block of a coding treeunit (CTU) of a current picture. In particular, at least some of thesearch areas may include samples of the current picture located outsideof the current CTU, and at least some of the search areas may notinclude samples of the current picture located outside of the currentCTU. The techniques of this disclosure may be used with screen contentcoding, including the support of possibly high bit depth (more than 8bit), different chroma sampling format such as 4:4:4, 4:2:2, 4:2:0,4:0:0, and other techniques.

As one example, a method includes determining, for each respectivecoding block of a plurality of coding blocks of a current coding treeunit (CTU) of video data in a current picture of the video data, arespective search area of a plurality of respective search areas,wherein the search areas of the plurality of search areas are alldifferent, wherein at least one of the plurality of search areasincludes samples of the current picture located outside of the currentCTU, and wherein at least one of the plurality of search areas does notinclude samples of the current picture located outside of the currentCTU; selecting, for each respective coding block and from within therespective search area for the respective coding block, a respectivepredictor block of a plurality of predictor blocks; and reconstructingsamples of each respective coding block based on samples included in acorresponding predictor block in the plurality of predictor blocks.

As another example, a device for coding video data includes a memoryconfigured to store the video data; and one or more processorsimplemented in circuitry and configured to: determine, for eachrespective coding block of a plurality of coding blocks of a currentcoding tree unit (CTU) of the video data in a current picture of videodata, a respective search area of a plurality of respective searchareas, wherein the search areas of the plurality of search areas are alldifferent, wherein at least one of the plurality of search areasincludes samples of the current picture located outside of the currentCTU, and wherein at least one of the plurality of search areas does notinclude samples of the current picture located outside of the currentCTU; select, for each respective coding block and from within therespective search area for the respective coding block, a respectivepredictor block of a plurality of predictor blocks; and reconstructsamples of each respective coding block based on samples included in acorresponding predictor block in the plurality of predictor blocks.

As another example, a video coder includes means for determining, foreach respective coding block of a plurality of coding blocks of acurrent coding tree unit (CTU) of video data in a current picture ofvideo data, a respective search area of a plurality of respective searchareas, wherein the search areas of the plurality of search areas are alldifferent, wherein at least one of the plurality of search areasincludes samples of the current picture located outside of the currentCTU, and wherein at least one of the plurality of search areas does notinclude samples of the current picture located outside of the currentCTU; means for selecting, for each respective coding block and fromwithin the respective search area for the respective coding block, arespective predictor block of a plurality of predictor blocks; and meansfor reconstructing samples of each respective coding block based onsamples included in a corresponding predictor block in the plurality ofpredictor blocks.

As another example, a computer-readable storage medium storesinstructions that, when executed, cause one or more processors to:determine, for each respective coding block of a plurality of codingblocks of a current coding tree unit (CTU) of video data in a currentpicture of video data, a respective search area of a plurality ofrespective search areas, wherein the search areas of the plurality ofsearch areas are all different, wherein at least one of the plurality ofsearch areas includes samples of the current picture located outside ofthe current CTU, and wherein at least one of the plurality of searchareas does not include samples of the current picture located outside ofthe current CTU; select, for each respective coding block and fromwithin the respective search area for the respective coding block, arespective predictor block of a plurality of predictor blocks; andreconstruct samples of each respective coding block based on samplesincluded in a corresponding predictor block in the plurality ofpredictor blocks.

The details of one or more examples are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description, drawings, and claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating an example video encoding anddecoding system that may perform the techniques of this disclosure.

FIG. 2 is a diagram illustrating an example of an intra block copyingprocess, in accordance with one or more techniques of this disclosure.

FIGS. 3A and 3B are conceptual diagrams illustrating an example quadtreebinary tree (QTBT) structure, and a corresponding coding tree unit(CTU).

FIG. 4 is a block diagram illustrating an example video encoder that mayperform the techniques of this disclosure.

FIG. 5 is a block diagram illustrating an example video decoder that mayperform the techniques of this disclosure.

FIG. 6 is a conceptual diagram illustrating a CTU coded using apipeline, in accordance with one or more techniques of this disclosure.

FIG. 7 is a conceptual diagram illustrating example search areas usedfor CPR, in accordance with one or more techniques of this disclosure.

FIG. 8 is a conceptual diagram illustrating example search areas usedfor CPR, in accordance with one or more techniques of this disclosure.

FIGS. 9A-9C are conceptual diagrams illustrating example search areasused for performing CPR with various scan orders, in accordance with oneor more techniques of this disclosure.

FIG. 10 is a conceptual diagram illustrating example search areas usedfor CPR, in accordance with one or more techniques of this disclosure.

FIG. 11 is a conceptual diagram illustrating example search areas usedfor CPR, in accordance with one or more techniques of this disclosure.

FIGS. 12A-12D are conceptual diagrams illustrating example search areasused for performing CPR for various coding blocks of a CTU, inaccordance with one or more techniques of this disclosure.

FIG. 13 is a flowchart illustrating an example method for encoding acurrent block.

FIG. 14 is a flowchart illustrating an example method for decoding acurrent block.

FIG. 15 is a flowchart illustrating an example method for predicting ablock of video data in a current picture using hybrid search areas, inaccordance with the techniques of this disclosure.

DETAILED DESCRIPTION

Video coding standards include ITU-T H.261, ISO/IEC MPEG-1 Visual, ITU-TH.262 or ISO/IEC MPEG-2 Visual, ITU-T H.263, ISO/IEC MPEG-4 Visual andITU-T H.264 (also known as ISO/IEC MPEG-4 AVC), including its ScalableVideo Coding (SVC) and Multiview Video Coding (MVC) extensions.

High-Efficiency Video Coding (HEVC), was finalized by the JointCollaboration Team on Video Coding (JCT-VC) of ITU-T Video CodingExperts Group (VCEG) and ISO/IEC Motion Picture Experts Group (MPEG) inApril 2013.

The Joint Video Experts Team (JVET), a collaborative team formed by MPEGand ITU-T Study Group 16's VCEG is recently working on a new videocoding standard to be known as Versatile Video Coding (VVC). The primaryobjective of VVC is to provide a significant improvement in compressionperformance over the existing HEVC standard, aiding in deployment ofhigher-quality video services and emerging applications such as 360°omnidirectional immersive multimedia and high-dynamic-range (HDR) video.The development of the VVC standard is expected to be completed in 2020.

Current picture referencing (CPR) or Intra block copy (IBC) (describedin X. Xu, S. Liu, T. Chuang, Y. Huang, S. Lei, K. Rapaka, C. Pang, V.Seregin, Y. Wang, and M. Karczewicz, “Intra Block Copy in HEVC ScreenContent Coding Extensions,” IEEE J. Emerg. Sel. Topics Circuits Syst.,vol. 6, no. 4, pp. 409-419, 2016) has been proposed during thestandardization of HEVC SCC extensions (see e.g., High Efficiency VideoCoding (HEVC), Rec. ITU-T H.265 and ISO/IEC 23008-2, December 2016). IBChas been proved to be efficient when coding of screen content videomaterials. This method was previously proposed in JVET-J0029 andJVET-J0050 to address the need for efficient screen content coding. Inthe 11^(st) JVET meeting, CPR mode (Xiaozhong Xu, Xiang Li and Shan Liu,“CE8-2.2: Current picture referencing using reference index signaling”,JVET-K0076, Ljubljana, SL, July 2018 (hereinafter “JVET-K0076”)) wasadopted into Benchmark Set (BMS) software of VVC for further evaluation.

The current picture reference (CPR) mode described in JVET-K0076 hasbeen adopted into the BMS software. In the CPR mode, a video coderpredicts an intra block copy (IBC) block in a current picture from analready decoded predictor block (before in-loop filtering, such as oneor both of adaptive loop filter (ALF) and Sample Adaptive Offset (SAO))of the current picture. For instance, to predict a current block usingthe CPR mode, a video encoder may select a predictor block from with ina reference area. The video encoder may select the predictor block as ablock in the reference area with that most closely match samples of thecurrent block (e.g., to reduce the size of residual data). The videoencoder may encode a vector (e.g., a block vector, a motion vector,etc.) that represents a displacement between the current block and theselected predictor block along with residual data that representsdifferences between samples of the predictor block and samples of thecurrent block. The video decoder may decode the current block using areciprocal process. For instance, the video decoder may decode thevector and the residual data, select the predictor block based on thevector, and reconstruct the samples of the current block based on thesamples of the predictor block and the residual data.

In the current CPR mode, the reference area (i.e., the area of thecurrent picture from which the predictor block may be selected) may berestricted to reconstructed samples of a current coding tree unit (CTU)that includes the block being predicted. As such, in the current CPRmore, a video coder may predict coding blocks of a particular CTU usingpredictor blocks located in the particular CTU. Restricting thereference area to the current CTU may reduce the memory needed topredict blocks using the CPR mode. For instance, restricting thereference area to the current CTU may enable a video coder to onlyaccess/store samples of the current CTU when coding the current CTU.However, this limitation may reduce the performance of CPR coding incomparison to having a larger reference area. In particular, restrictingthe reference area to the current CTU may reduce the probability that apredictor block with samples matching the current block may be utilized,which may result in an increase in residual data size. Increasing thesize of the residual data may undesirably decrease the coding efficiency(e.g., require more bits to represent the video data).

In accordance with one or more techniques of this disclosure, a videocoder (e.g., video encoder 200 and/or video decoder 300) may utilizehybrid search areas when coding blocks of video data using the CPR mode.For instance, the video coder may utilize a different search area foreach coding block of a CTU of a current picture. The search areas may beconsidered hybrid in that the search area for at least one coding blockincludes samples of the current picture located outside of the currentCTU, and the search area for at least one coding block does not includesamples of the current picture located outside of the current CTU. Byutilizing hybrid search areas, the video coder may balance the memoryused to perform CPR with the coding efficiency.

FIG. 1 is a block diagram illustrating an example video encoding anddecoding system 100 that may perform the techniques of this disclosure.The techniques of this disclosure are generally directed to coding(encoding and/or decoding) video data. In general, video data includesany data for processing a video. Thus, video data may include raw,unencoded video, encoded video, decoded (e.g., reconstructed) video, andvideo metadata, such as signaling data.

As shown in FIG. 1, system 100 includes a source device 102 thatprovides encoded video data to be decoded and displayed by a destinationdevice 116, in this example. In particular, source device 102 providesthe video data to destination device 116 via a computer-readable medium110. Source device 102 and destination device 116 may comprise any of awide range of devices, including desktop computers, notebook (i.e.,laptop) computers, tablet computers, set-top boxes, telephone handsetssuch as smartphones, televisions, cameras, display devices, digitalmedia players, video gaming consoles, video streaming device, or thelike. In some cases, source device 102 and destination device 116 may beequipped for wireless communication, and thus may be referred to aswireless communication devices.

In the example of FIG. 1, source device 102 includes video source 104,memory 106, video encoder 200, and output interface 108. Destinationdevice 116 includes input interface 122, video decoder 300, memory 120,and display device 118. In accordance with this disclosure, videoencoder 200 of source device 102 and video decoder 300 of destinationdevice 116 may be configured to apply the techniques for hybrid searchareas for CPR. Thus, source device 102 represents an example of a videoencoding device, while destination device 116 represents an example of avideo decoding device. In other examples, a source device and adestination device may include other components or arrangements. Forexample, source device 102 may receive video data from an external videosource, such as an external camera. Likewise, destination device 116 mayinterface with an external display device, rather than include anintegrated display device.

System 100 as shown in FIG. 1 is merely one example. In general, anydigital video encoding and/or decoding device may perform techniques forhybrid search areas for CPR. Source device 102 and destination device116 are merely examples of such coding devices in which source device102 generates coded video data for transmission to destination device116. This disclosure refers to a “coding” device as a device thatperforms coding (encoding and/or decoding) of data. Thus, video encoder200 and video decoder 300 represent examples of coding devices, inparticular, a video encoder and a video decoder, respectively. In someexamples, source device 102 and destination device 116 may operate in asubstantially symmetrical manner such that each of source device 102 anddestination device 116 includes video encoding and decoding components.Hence, system 100 may support one-way or two-way video transmissionbetween source device 102 and destination device 116, e.g., for videostreaming, video playback, video broadcasting, or video telephony.

In general, video source 104 represents a source of video data (i.e.,raw, unencoded video data) and provides a sequential series of pictures(also referred to as “frames”) of the video data to video encoder 200,which encodes data for the pictures. Video source 104 of source device102 may include a video capture device, such as a video camera, a videoarchive containing previously captured raw video, and/or a video feedinterface to receive video from a video content provider. As a furtheralternative, video source 104 may generate computer graphics-based dataas the source video, or a combination of live video, archived video, andcomputer-generated video. In each case, video encoder 200 encodes thecaptured, pre-captured, or computer-generated video data. Video encoder200 may rearrange the pictures from the received order (sometimesreferred to as “display order”) into a coding order for coding. Videoencoder 200 may generate a bitstream including encoded video data.Source device 102 may then output the encoded video data via outputinterface 108 onto computer-readable medium 110 for reception and/orretrieval by, e.g., input interface 122 of destination device 116.

Memory 106 of source device 102 and memory 120 of destination device 116represent general purpose memories. In some examples, memories 106, 120may store raw video data, e.g., raw video from video source 104 and raw,decoded video data from video decoder 300. Additionally oralternatively, memories 106, 120 may store software instructionsexecutable by, e.g., video encoder 200 and video decoder 300,respectively. Although memory 106 and memory 120 are shown separatelyfrom video encoder 200 and video decoder 300 in this example, it shouldbe understood that video encoder 200 and video decoder 300 may alsoinclude internal memories for functionally similar or equivalentpurposes. Furthermore, memories 106, 120 may store encoded video data,e.g., output from video encoder 200 and input to video decoder 300. Insome examples, portions of memories 106, 120 may be allocated as one ormore video buffers, e.g., to store raw, decoded, and/or encoded videodata.

Computer-readable medium 110 may represent any type of medium or devicecapable of transporting the encoded video data from source device 102 todestination device 116. In one example, computer-readable medium 110represents a communication medium to enable source device 102 totransmit encoded video data directly to destination device 116 inreal-time, e.g., via a radio frequency network or computer-basednetwork. Output interface 108 may modulate a transmission signalincluding the encoded video data, and input interface 122 may demodulatethe received transmission signal, according to a communication standard,such as a wireless communication protocol. The communication medium maycomprise any wireless or wired communication medium, such as a radiofrequency (RF) spectrum or one or more physical transmission lines. Thecommunication medium may form part of a packet-based network, such as alocal area network, a wide-area network, or a global network such as theInternet. The communication medium may include routers, switches, basestations, or any other equipment that may be useful to facilitatecommunication from source device 102 to destination device 116.

In some examples, source device 102 may output encoded data from outputinterface 108 to storage device 112. Similarly, destination device 116may access encoded data from storage device 112 via input interface 122.Storage device 112 may include any of a variety of distributed orlocally accessed data storage media such as a hard drive, Blu-ray discs,DVDs, CD-ROMs, flash memory, volatile or non-volatile memory, or anyother suitable digital storage media for storing encoded video data.

In some examples, source device 102 may output encoded video data tofile server 114 or another intermediate storage device that may storethe encoded video generated by source device 102. Destination device 116may access stored video data from file server 114 via streaming ordownload. File server 114 may be any type of server device capable ofstoring encoded video data and transmitting that encoded video data tothe destination device 116. File server 114 may represent a web server(e.g., for a website), a File Transfer Protocol (FTP) server, a contentdelivery network device, or a network attached storage (NAS) device.Destination device 116 may access encoded video data from file server114 through any standard data connection, including an Internetconnection. This may include a wireless channel (e.g., a Wi-Ficonnection), a wired connection (e.g., digital subscriber line (DSL),cable modem, etc.), or a combination of both that is suitable foraccessing encoded video data stored on file server 114. File server 114and input interface 122 may be configured to operate according to astreaming transmission protocol, a download transmission protocol, or acombination thereof.

Output interface 108 and input interface 122 may represent wirelesstransmitters/receivers, modems, wired networking components (e.g.,Ethernet cards), wireless communication components that operateaccording to any of a variety of IEEE 802.11 standards, or otherphysical components. In examples where output interface 108 and inputinterface 122 comprise wireless components, output interface 108 andinput interface 122 may be configured to transfer data, such as encodedvideo data, according to a cellular communication standard, such as 4G,4G-LTE (Long-Term Evolution), LTE Advanced, 5G, or the like. In someexamples where output interface 108 comprises a wireless transmitter,output interface 108 and input interface 122 may be configured totransfer data, such as encoded video data, according to other wirelessstandards, such as an IEEE 802.11 specification, an IEEE 802.15specification (e.g., ZigBee™), a Bluetooth™ standard, or the like. Insome examples, source device 102 and/or destination device 116 mayinclude respective system-on-a-chip (SoC) devices. For example, sourcedevice 102 may include an SoC device to perform the functionalityattributed to video encoder 200 and/or output interface 108, anddestination device 116 may include an SoC device to perform thefunctionality attributed to video decoder 300 and/or input interface122.

The techniques of this disclosure may be applied to video coding insupport of any of a variety of multimedia applications, such asover-the-air television broadcasts, cable television transmissions,satellite television transmissions, Internet streaming videotransmissions, such as dynamic adaptive streaming over HTTP (DASH),digital video that is encoded onto a data storage medium, decoding ofdigital video stored on a data storage medium, or other applications.

Input interface 122 of destination device 116 receives an encoded videobitstream from computer-readable medium 110 (e.g., a communicationmedium, storage device 112, file server 114, or the like). The encodedvideo bitstream may include signaling information defined by videoencoder 200, which is also used by video decoder 300, such as syntaxelements having values that describe characteristics and/or processingof video blocks or other coded units (e.g., slices, pictures, groups ofpictures, sequences, or the like). Display device 118 displays decodedpictures of the decoded video data to a user. Display device 118 mayrepresent any of a variety of display devices such as a cathode ray tube(CRT), a liquid crystal display (LCD), a plasma display, an organiclight emitting diode (OLED) display, or another type of display device.

Although not shown in FIG. 1, in some examples, video encoder 200 andvideo decoder 300 may each be integrated with an audio encoder and/oraudio decoder, and may include appropriate MUX-DEMUX units, or otherhardware and/or software, to handle multiplexed streams including bothaudio and video in a common data stream. If applicable, MUX-DEMUX unitsmay conform to the ITU H.223 multiplexer protocol, or other protocolssuch as the user datagram protocol (UDP).

Video encoder 200 and video decoder 300 each may be implemented as anyof a variety of suitable encoder and/or decoder circuitry, such as oneor more microprocessors, digital signal processors (DSPs), applicationspecific integrated circuits (ASICs), field programmable gate arrays(FPGAs), discrete logic, software, hardware, firmware or anycombinations thereof. When the techniques are implemented partially insoftware, a device may store instructions for the software in asuitable, non-transitory computer-readable medium and execute theinstructions in hardware using one or more processors to perform thetechniques of this disclosure. Each of video encoder 200 and videodecoder 300 may be included in one or more encoders or decoders, eitherof which may be integrated as part of a combined encoder/decoder (CODEC)in a respective device. A device including video encoder 200 and/orvideo decoder 300 may comprise an integrated circuit, a microprocessor,and/or a wireless communication device, such as a cellular telephone.

Video encoder 200 and video decoder 300 may operate according to a videocoding standard, such as ITU-T H.265, also referred to as HighEfficiency Video Coding (HEVC) or extensions thereto, such as themulti-view and/or scalable video coding extensions. Alternatively, videoencoder 200 and video decoder 300 may operate according to otherproprietary or industry standards, such as the Joint Exploration TestModel (JEM) or ITU-T H.266, also referred to as Versatile Video Coding(VVC). A recent draft of the VVC standard is described in Bross, et al.“Versatile Video Coding (Draft 6),” Joint Video Experts Team (WET) ofITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG 11, 11th Meeting: Ljubljana,SI, 10-18 Jul. 2018, JVET-K1001-v6 (hereinafter “VVC Draft 2”). Thetechniques of this disclosure, however, are not limited to anyparticular coding standard.

In general, video encoder 200 and video decoder 300 may performblock-based coding of pictures. The term “block” generally refers to astructure including data to be processed (e.g., encoded, decoded, orotherwise used in the encoding and/or decoding process). For example, ablock may include a two-dimensional matrix of samples of luminanceand/or chrominance data. In general, video encoder 200 and video decoder300 may code video data represented in a YUV (e.g., Y, Cb, Cr) format.That is, rather than coding red, green, and blue (RGB) data for samplesof a picture, video encoder 200 and video decoder 300 may code luminanceand chrominance components, where the chrominance components may includeboth red hue and blue hue chrominance components. In some examples,video encoder 200 converts received RGB formatted data to a YUVrepresentation prior to encoding, and video decoder 300 converts the YUVrepresentation to the RGB format. Alternatively, pre- andpost-processing units (not shown) may perform these conversions.

This disclosure may generally refer to coding (e.g., encoding anddecoding) of pictures to include the process of encoding or decodingdata of the picture. Similarly, this disclosure may refer to coding ofblocks of a picture to include the process of encoding or decoding datafor the blocks, e.g., prediction and/or residual coding. An encodedvideo bitstream generally includes a series of values for syntaxelements representative of coding decisions (e.g., coding modes) andpartitioning of pictures into blocks. Thus, references to coding apicture or a block should generally be understood as coding values forsyntax elements forming the picture or block.

HEVC defines various blocks, including coding units (CUs), predictionunits (PUs), and transform units (TUs). According to HEVC, a video coder(such as video encoder 200) partitions a coding tree unit (CTU) into CUsaccording to a quadtree structure. That is, the video coder partitionsCTUs and CUs into four equal, non-overlapping squares, and each node ofthe quadtree has either zero or four child nodes. Nodes without childnodes may be referred to as “leaf nodes,” and CUs of such leaf nodes mayinclude one or more PUs and/or one or more TUs. The video coder mayfurther partition PUs and TUs. For example, in HEVC, a residual quadtree(RQT) represents partitioning of TUs. In HEVC, PUs representinter-prediction data, while TUs represent residual data. CUs that areintra-predicted include intra-prediction information, such as anintra-mode indication.

As another example, video encoder 200 and video decoder 300 may beconfigured to operate according to JEM or VVC. According to JEM or VVC,a video coder (such as video encoder 200) partitions a picture into aplurality of coding tree units (CTUs). Video encoder 200 may partition aCTU according to a tree structure, such as a quadtree-binary tree (QTBT)structure or Multi-Type Tree (MTT) structure. The QTBT structure removesthe concepts of multiple partition types, such as the separation betweenCUs, PUs, and TUs of HEVC. A QTBT structure includes two levels: a firstlevel partitioned according to quadtree partitioning, and a second levelpartitioned according to binary tree partitioning. A root node of theQTBT structure corresponds to a CTU. Leaf nodes of the binary treescorrespond to coding units (CUs).

In an MTT partitioning structure, blocks may be partitioned using aquadtree (QT) partition, a binary tree (BT) partition, and one or moretypes of triple tree (TT) (also called ternary tree (TT)) partitions. Atriple or ternary tree partition is a partition where a block is splitinto three sub-blocks. In some examples, a triple or ternary treepartition divides a block into three sub-blocks without dividing theoriginal block through the center. The partitioning types in MTT (e.g.,QT, BT, and TT), may be symmetrical or asymmetrical.

In some examples, video encoder 200 and video decoder 300 may use asingle QTBT or MTT structure to represent each of the luminance andchrominance components, while in other examples, video encoder 200 andvideo decoder 300 may use two or more QTBT or MTT structures, such asone QTBT/MTT structure for the luminance component and another QTBT/MTTstructure for both chrominance components (or two QTBT/MTT structuresfor respective chrominance components).

Video encoder 200 and video decoder 300 may be configured to usequadtree partitioning per HEVC, QTBT partitioning, MTT partitioning, orother partitioning structures. For purposes of explanation, thedescription of the techniques of this disclosure is presented withrespect to QTBT partitioning. However, it should be understood that thetechniques of this disclosure may also be applied to video codersconfigured to use quadtree partitioning, or other types of partitioningas well.

The blocks (e.g., CTUs or CUs) may be grouped in various ways in apicture. As one example, a brick may refer to a rectangular region ofCTU rows within a particular tile in a picture. A tile may be arectangular region of CTUs within a particular tile column and aparticular tile row in a picture. A tile column refers to a rectangularregion of CTUs having a height equal to the height of the picture and awidth specified by syntax elements (e.g., such as in a picture parameterset). A tile row refers to a rectangular region of CTUs having a heightspecified by syntax elements (e.g., such as in a picture parameter set)and a width equal to the width of the picture.

In some examples, a tile may be partitioned into multiple bricks, eachof which may include one or more CTU rows within the tile. A tile thatis not partitioned into multiple bricks may also be referred to as abrick. However, a brick that is a true subset of a tile may not bereferred to as a tile.

The bricks in a picture may also be arranged in a slice. A slice may bean integer number of bricks of a picture that may be exclusivelycontained in a single network abstraction layer (NAL) unit. In someexamples, a slice includes either a number of complete tiles or only aconsecutive sequence of complete bricks of one tile.

This disclosure may use “N×N” and “N by N” interchangeably to refer tothe sample dimensions of a block (such as a CU or other video block) interms of vertical and horizontal dimensions, e.g., 16×16 samples or 16by 16 samples. In general, a 16×16 CU will have 16 samples in a verticaldirection (y=16) and 16 samples in a horizontal direction (x=16).Likewise, an N×N CU generally has N samples in a vertical direction andN samples in a horizontal direction, where N represents a nonnegativeinteger value. The samples in a CU may be arranged in rows and columns.Moreover, CUs need not necessarily have the same number of samples inthe horizontal direction as in the vertical direction. For example, CUsmay comprise N×M samples, where M is not necessarily equal to N.

Video encoder 200 encodes video data for CUs representing predictionand/or residual information, and other information. The predictioninformation indicates how the CU is to be predicted in order to form aprediction block for the CU. The residual information generallyrepresents sample-by-sample differences between samples of the CU priorto encoding and the prediction block.

To predict a CU, video encoder 200 may generally form a prediction blockfor the CU through inter-prediction or intra-prediction.Inter-prediction generally refers to predicting the CU from data of apreviously coded picture, whereas intra-prediction generally refers topredicting the CU from previously coded data of the same picture. Toperform inter-prediction, video encoder 200 may generate the predictionblock using one or more motion vectors. Video encoder 200 may generallyperform a motion search to identify a reference block that closelymatches the CU, e.g., in terms of differences between the CU and thereference block. Video encoder 200 may calculate a difference metricusing a sum of absolute difference (SAD), sum of squared differences(SSD), mean absolute difference (MAD), mean squared differences (MSD),or other such difference calculations to determine whether a referenceblock closely matches the current CU. In some examples, video encoder200 may predict the current CU using uni-directional prediction orbi-directional prediction.

Some examples of JEM and VVC also provide an affine motion compensationmode, which may be considered an inter-prediction mode. In affine motioncompensation mode, video encoder 200 may determine two or more motionvectors that represent non-translational motion, such as zoom in or out,rotation, perspective motion, or other irregular motion types.

To perform intra-prediction, video encoder 200 may select anintra-prediction mode to generate the prediction block. Some examples ofJEM and VVC provide sixty-seven intra-prediction modes, includingvarious directional modes, as well as planar mode and DC mode. Ingeneral, video encoder 200 selects an intra-prediction mode thatdescribes neighboring samples to a current block (e.g., a block of a CU)from which to predict samples of the current block. Such samples maygenerally be above, above and to the left, or to the left of the currentblock in the same picture as the current block, assuming video encoder200 codes CTUs and CUs in raster scan order (left to right, top tobottom).

Video encoder 200 encodes data representing the prediction mode for acurrent block. For example, for inter-prediction modes, video encoder200 may encode data representing which of the various availableinter-prediction modes is used, as well as motion information for thecorresponding mode. For uni-directional or bi-directionalinter-prediction, for example, video encoder 200 may encode motionvectors using advanced motion vector prediction (AMVP) or merge mode.Video encoder 200 may use similar modes to encode motion vectors foraffine motion compensation mode.

Following prediction, such as intra-prediction or inter-prediction of ablock, video encoder 200 may calculate residual data for the block. Theresidual data, such as a residual block, represents sample by sampledifferences between the block and a prediction block for the block,formed using the corresponding prediction mode. Video encoder 200 mayapply one or more transforms to the residual block, to producetransformed data in a transform domain instead of the sample domain. Forexample, video encoder 200 may apply a discrete cosine transform (DCT),an integer transform, a wavelet transform, or a conceptually similartransform to residual video data. Additionally, video encoder 200 mayapply a secondary transform following the first transform, such as amode-dependent non-separable secondary transform (MDNSST), a signaldependent transform, a Karhunen-Loeve transform (KLT), or the like.Video encoder 200 produces transform coefficients following applicationof the one or more transforms.

As noted above, following any transforms to produce transformcoefficients, video encoder 200 may perform quantization of thetransform coefficients. Quantization generally refers to a process inwhich transform coefficients are quantized to possibly reduce the amountof data used to represent the transform coefficients, providing furthercompression. By performing the quantization process, video encoder 200may reduce the bit depth associated with some or all of the transformcoefficients. For example, video encoder 200 may round an n-bit valuedown to an m-bit value during quantization, where n is greater than m.In some examples, to perform quantization, video encoder 200 may performa bitwise right-shift of the value to be quantized.

Following quantization, video encoder 200 may scan the transformcoefficients, producing a one-dimensional vector from thetwo-dimensional matrix including the quantized transform coefficients.The scan may be designed to place higher energy (and therefore lowerfrequency) transform coefficients at the front of the vector and toplace lower energy (and therefore higher frequency) transformcoefficients at the back of the vector. In some examples, video encoder200 may utilize a predefined scan order to scan the quantized transformcoefficients to produce a serialized vector, and then entropy encode thequantized transform coefficients of the vector. In other examples, videoencoder 200 may perform an adaptive scan. After scanning the quantizedtransform coefficients to form the one-dimensional vector, video encoder200 may entropy encode the one-dimensional vector, e.g., according tocontext-adaptive binary arithmetic coding (CABAC). Video encoder 200 mayalso entropy encode values for syntax elements describing metadataassociated with the encoded video data for use by video decoder 300 indecoding the video data.

To perform CABAC, video encoder 200 may assign a context within acontext model to a symbol to be transmitted. The context may relate to,for example, whether neighboring values of the symbol are zero-valued ornot. The probability determination may be based on a context assigned tothe symbol.

Video encoder 200 may further generate syntax data, such as block-basedsyntax data, picture-based syntax data, and sequence-based syntax data,to video decoder 300, e.g., in a picture header, a block header, a sliceheader, or other syntax data, such as a sequence parameter set (SPS),picture parameter set (PPS), or video parameter set (VPS). Video decoder300 may likewise decode such syntax data to determine how to decodecorresponding video data.

In this manner, video encoder 200 may generate a bitstream includingencoded video data, e.g., syntax elements describing partitioning of apicture into blocks (e.g., CUs) and prediction and/or residualinformation for the blocks. Ultimately, video decoder 300 may receivethe bitstream and decode the encoded video data.

In general, video decoder 300 performs a reciprocal process to thatperformed by video encoder 200 to decode the encoded video data of thebitstream. For example, video decoder 300 may decode values for syntaxelements of the bitstream using CABAC in a manner substantially similarto, albeit reciprocal to, the CABAC encoding process of video encoder200. The syntax elements may define partitioning information of apicture into CTUs, and partitioning of each CTU according to acorresponding partition structure, such as a QTBT structure, to defineCUs of the CTU. The syntax elements may further define prediction andresidual information for blocks (e.g., CUs) of video data.

The residual information may be represented by, for example, quantizedtransform coefficients. Video decoder 300 may inverse quantize andinverse transform the quantized transform coefficients of a block toreproduce a residual block for the block. Video decoder 300 uses asignaled prediction mode (intra- or inter-prediction) and relatedprediction information (e.g., motion information for inter-prediction)to form a prediction block for the block. Video decoder 300 may thencombine the prediction block and the residual block (on asample-by-sample basis) to reproduce the original block. Video decoder300 may perform additional processing, such as performing a deblockingprocess to reduce visual artifacts along boundaries of the block.

FIG. 2 is a diagram illustrating an example of a current picturereference (CPR) coding process, in accordance with one or moretechniques of this disclosure. According to one example CPR process,video encoder 200 may select a predictor video block, e.g., from a setof previously coded and reconstructed blocks of video data located in asearch area. In the example of FIG. 1, search area 8 includes the set ofpreviously coded and reconstructed video blocks. The blocks in thesearch area 8 may represent blocks that have been decoded andreconstructed by video decoder 300 and stored in decoded picture buffer314, or blocks that have been decoded and reconstructed in thereconstruction loop of video encoder 200 and stored in decoded picturebuffer 218. Current block 2 represents a current block of video data tobe coded. Predictor block 4 represents a reconstructed video block, inthe same picture as current block 2, which is used for Intra BCprediction of current block 2.

In the example CPR process, video encoder 200 may determine and encodemotion vector 6, which indicates the position of predictor block 4relative to current block 2, together with the residue signal. Forinstance, as illustrated by FIG. 1, motion vector 6 may indicate theposition of the upper-left corner of predictor block 4 relative to theupper-left corner of current block 2. Motion vector 6 may also bereferred to as an offset vector, displacement vector, or block vector(BV). Video decoder 300 may utilize the encoded information for decodingthe current block.

As discussed above, in the current CPR mode, the reference area (e.g.,search area 8) may be restricted to reconstructed samples of a currentcoding tree unit (CTU) that includes the block being predicted (e.g., aCTU that includes current block 2). This restriction may be advantageousin that it reduces the amount of memory required to perform CPR.However, as also discussed above, this restriction may reduce the codingefficiency of CPR.

In accordance with one or more techniques of this disclosure, a videocoder (e.g., video encoder 200 and/or video decoder 300) may utilizehybrid search areas when coding blocks of video data using the CPR mode.For instance, the video coder may determine, for each respective codingblock of a plurality of coding blocks of a current coding tree unit(CTU) of video data in a current picture of video data, a respectivesearch area of a plurality of respective search areas. The search areasof the plurality of search areas may all be different. For instance, thesearch area used for any given coding block of a CTU may be differentthat the search area used for any other coding block of the CTU. Thesearch areas may be considered hybrid in that the search area for atleast one coding block includes samples of the current picture locatedoutside of the current CTU, and the search area for at least one codingblock does not include samples of the current picture located outside ofthe current CTU. By utilizing hybrid search areas, the video coder maybalance the memory used to perform CPR with the coding efficiency.

This disclosure may generally refer to “signaling” certain information,such as syntax elements. The term “signaling” may generally refer to thecommunication of values for syntax elements and/or other data used todecode encoded video data. That is, video encoder 200 may signal valuesfor syntax elements in the bitstream. In general, signaling refers togenerating a value in the bitstream. As noted above, source device 102may transport the bitstream to destination device 116 substantially inreal time, or not in real time, such as might occur when storing syntaxelements to storage device 112 for later retrieval by destination device116.

FIGS. 3A and 3B are conceptual diagrams illustrating an example quadtreebinary tree (QTBT) structure 130, and a corresponding coding tree unit(CTU) 132. The solid lines represent quadtree splitting, and dottedlines indicate binary tree splitting. In each split (i.e., non-leaf)node of the binary tree, one flag is signaled to indicate whichsplitting type (i.e., horizontal or vertical) is used, where 0 indicateshorizontal splitting and 1 indicates vertical splitting in this example.For the quadtree splitting, there is no need to indicate the splittingtype, because quadtree nodes split a block horizontally and verticallyinto 4 sub-blocks with equal size. Accordingly, video encoder 200 mayencode, and video decoder 300 may decode, syntax elements (such assplitting information) for a region tree level of QTBT structure 130(i.e., the solid lines) and syntax elements (such as splittinginformation) for a prediction tree level of QTBT structure 130 (i.e.,the dashed lines). Video encoder 200 may encode, and video decoder 300may decode, video data, such as prediction and transform data, for CUsrepresented by terminal leaf nodes of QTBT structure 130.

In general, CTU 132 of FIG. 3B may be associated with parametersdefining sizes of blocks corresponding to nodes of QTBT structure 130 atthe first and second levels. These parameters may include a CTU size(representing a size of CTU 132 in samples), a minimum quadtree size(MinQTSize, representing a minimum allowed quadtree leaf node size), amaximum binary tree size (MaxBTSize, representing a maximum allowedbinary tree root node size), a maximum binary tree depth (MaxBTDepth,representing a maximum allowed binary tree depth), and a minimum binarytree size (MinBTSize, representing the minimum allowed binary tree leafnode size).

The root node of a QTBT structure corresponding to a CTU may have fourchild nodes at the first level of the QTBT structure, each of which maybe partitioned according to quadtree partitioning. That is, nodes of thefirst level are either leaf nodes (having no child nodes) or have fourchild nodes. The example of QTBT structure 130 represents such nodes asincluding the parent node and child nodes having solid lines forbranches. If nodes of the first level are not larger than the maximumallowed binary tree root node size (MaxBTSize), then the nodes can befurther partitioned by respective binary trees. The binary treesplitting of one node can be iterated until the nodes resulting from thesplit reach the minimum allowed binary tree leaf node size (MinBTSize)or the maximum allowed binary tree depth (MaxBTDepth). The example ofQTBT structure 130 represents such nodes as having dashed lines forbranches. The binary tree leaf node is referred to as a coding unit(CU), which is used for prediction (e.g., intra-picture or inter-pictureprediction) and transform, without any further partitioning. Asdiscussed above, CUs may also be referred to as “video blocks,” “codingblocks,” or “blocks.”

In one example of the QTBT partitioning structure, the CTU size is setas 128×128 (luma samples and two corresponding 64×64 chroma samples),the MinQTSize is set as 16×16, the MaxBTSize is set as 64×64, theMinBTSize (for both width and height) is set as 4, and the MaxBTDepth isset as 4. The quadtree partitioning is applied to the CTU first togenerate quad-tree leaf nodes. The quadtree leaf nodes may have a sizefrom 16×16 (i.e., the MinQTSize) to 128×128 (i.e., the CTU size). If theleaf quadtree node is 128×128, the leaf quadtree node will not befurther split by the binary tree, because the size exceeds the MaxBTSize(i.e., 64×64, in this example). Otherwise, the leaf quadtree node willbe further partitioned by the binary tree. Therefore, the quadtree leafnode is also the root node for the binary tree and has the binary treedepth as 0. When the binary tree depth reaches MaxBTDepth (4, in thisexample), no further splitting is permitted. When the binary tree nodehas a width equal to MinBTSize (4, in this example), it implies nofurther horizontal splitting is permitted. Similarly, a binary tree nodehaving a height equal to MinBTSize implies no further vertical splittingis permitted for that binary tree node. As noted above, leaf nodes ofthe binary tree are referred to as CUs, and are further processedaccording to prediction and transform without further partitioning.

In some examples, the video coder may perform block compensation withinteger block compensation for the luma components that are coded withCPR. In this way, the video coder may avoid performing interpolation forluma components. In some examples, the video coder may perform blockcompensation for chroma components using sub-pel block compensation. Assuch, the video coder may perform interpolation for chroma components.

FIG. 4 is a block diagram illustrating an example video encoder 200 thatmay perform the techniques of this disclosure. FIG. 4 is provided forpurposes of explanation and should not be considered limiting of thetechniques as broadly exemplified and described in this disclosure. Forpurposes of explanation, this disclosure describes video encoder 200 inthe context of video coding standards such as the HEVC video codingstandard and the H.266 video coding standard in development. However,the techniques of this disclosure are not limited to these video codingstandards, and are applicable generally to video encoding and decoding.

In the example of FIG. 4, video encoder 200 includes video data memory230, mode selection unit 202, residual generation unit 204, transformprocessing unit 206, quantization unit 208, inverse quantization unit210, inverse transform processing unit 212, reconstruction unit 214,filter unit 216, decoded picture buffer (DPB) 218, and entropy encodingunit 220. Any or all of video data memory 230, mode selection unit 202,residual generation unit 204, transform processing unit 206,quantization unit 208, inverse quantization unit 210, inverse transformprocessing unit 212, reconstruction unit 214, filter unit 216, DPB 218,and entropy encoding unit 220 may be implemented in one or moreprocessors or in processing circuitry. For instance, the units of videoencoder 200 may be implemented as one or more circuits or logic elementsas part of hardware circuitry, or as part of a processor, ASIC, of FPGA.Moreover, video encoder 200 may include additional or alternativeprocessors or processing circuitry to perform these and other functions.

Video data memory 230 may store video data to be encoded by thecomponents of video encoder 200. Video encoder 200 may receive the videodata stored in video data memory 230 from, for example, video source 104(FIG. 1). DPB 218 may act as a reference picture memory that storesreference video data for use in prediction of subsequent video data byvideo encoder 200. Video data memory 230 and DPB 218 may be formed byany of a variety of memory devices, such as dynamic random access memory(DRAM), including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM),resistive RAM (RRAM), or other types of memory devices. Video datamemory 230 and DPB 218 may be provided by the same memory device orseparate memory devices. In various examples, video data memory 230 maybe on-chip with other components of video encoder 200, as illustrated,or off-chip relative to those components.

In this disclosure, reference to video data memory 230 should not beinterpreted as being limited to memory internal to video encoder 200,unless specifically described as such, or memory external to videoencoder 200, unless specifically described as such. Rather, reference tovideo data memory 230 should be understood as reference memory thatstores video data that video encoder 200 receives for encoding (e.g.,video data for a current block that is to be encoded). Memory 106 ofFIG. 1 may also provide temporary storage of outputs from the variousunits of video encoder 200.

The various units of FIG. 4 are illustrated to assist with understandingthe operations performed by video encoder 200. The units may beimplemented as fixed-function circuits, programmable circuits, or acombination thereof. Fixed-function circuits refer to circuits thatprovide particular functionality, and are preset on the operations thatcan be performed. Programmable circuits refer to circuits that can beprogrammed to perform various tasks, and provide flexible functionalityin the operations that can be performed. For instance, programmablecircuits may execute software or firmware that cause the programmablecircuits to operate in the manner defined by instructions of thesoftware or firmware. Fixed-function circuits may execute softwareinstructions (e.g., to receive parameters or output parameters), but thetypes of operations that the fixed-function circuits perform aregenerally immutable. In some examples, one or more of the units may bedistinct circuit blocks (fixed-function or programmable), and in someexamples, one or more of the units may be integrated circuits.

Video encoder 200 may include arithmetic logic units (ALUs), elementaryfunction units (EFUs), digital circuits, analog circuits, and/orprogrammable cores, formed from programmable circuits. In examples wherethe operations of video encoder 200 are performed using softwareexecuted by the programmable circuits, memory 106 (FIG. 1) may store theinstructions (e.g., object code) of the software that video encoder 200receives and executes, or another memory within video encoder 200 (notshown) may store such instructions.

Video data memory 230 is configured to store received video data. Videoencoder 200 may retrieve a picture of the video data from video datamemory 230 and provide the video data to residual generation unit 204and mode selection unit 202. Video data in video data memory 230 may beraw video data that is to be encoded.

Mode selection unit 202 includes a motion estimation unit 222, motioncompensation unit 224, and an intra-prediction unit 226. Mode selectionunit 202 may include additional functional units to perform videoprediction in accordance with other prediction modes. As examples, modeselection unit 202 may include a palette unit, an intra-block copy unit(which may be part of motion estimation unit 222 and/or motioncompensation unit 224), an affine unit, a linear model (LM) unit, or thelike.

Mode selection unit 202 generally coordinates multiple encoding passesto test combinations of encoding parameters and resultingrate-distortion values for such combinations. The encoding parametersmay include partitioning of CTUs into CUs, prediction modes for the CUs,transform types for residual data of the CUs, quantization parametersfor residual data of the CUs, and so on. Mode selection unit 202 mayultimately select the combination of encoding parameters havingrate-distortion values that are better than the other testedcombinations.

Video encoder 200 may partition a picture retrieved from video datamemory 230 into a series of CTUs, and encapsulate one or more CTUswithin a slice. Mode selection unit 202 may partition a CTU of thepicture in accordance with a tree structure, such as the QTBT structureor the quad-tree structure of HEVC described above. As described above,video encoder 200 may form one or more CUs from partitioning a CTUaccording to the tree structure. Such a CU may also be referred togenerally as a “video block” or “block.”

In general, mode selection unit 202 also controls the components thereof(e.g., motion estimation unit 222, motion compensation unit 224, andintra-prediction unit 226) to generate a prediction block for a currentblock (e.g., a current CU, or in HEVC, the overlapping portion of a PUand a TU). For inter-prediction of a current block, motion estimationunit 222 may perform a motion search to identify one or more closelymatching reference blocks in one or more reference pictures (e.g., oneor more previously coded pictures stored in DPB 218). In particular,motion estimation unit 222 may calculate a value representative of howsimilar a potential reference block is to the current block, e.g.,according to sum of absolute difference (SAD), sum of squareddifferences (SSD), mean absolute difference (MAD), mean squareddifferences (MSD), or the like. Motion estimation unit 222 may generallyperform these calculations using sample-by-sample differences betweenthe current block and the reference block being considered. Motionestimation unit 222 may identify a reference block having a lowest valueresulting from these calculations, indicating a reference block thatmost closely matches the current block.

Motion estimation unit 222 may form one or more motion vectors (MVs)that defines the positions of the reference blocks in the referencepictures relative to the position of the current block in a currentpicture. Motion estimation unit 222 may then provide the motion vectorsto motion compensation unit 224. For example, for uni-directionalinter-prediction, motion estimation unit 222 may provide a single motionvector, whereas for bi-directional inter-prediction, motion estimationunit 222 may provide two motion vectors. Motion compensation unit 224may then generate a prediction block using the motion vectors. Forexample, motion compensation unit 224 may retrieve data of the referenceblock using the motion vector. As another example, if the motion vectorhas fractional sample precision, motion compensation unit 224 mayinterpolate values for the prediction block according to one or moreinterpolation filters. Moreover, for bi-directional inter-prediction,motion compensation unit 224 may retrieve data for two reference blocksidentified by respective motion vectors and combine the retrieved data,e.g., through sample-by-sample averaging or weighted averaging.

As another example, for intra-prediction, or intra-prediction coding,intra-prediction unit 226 may generate the prediction block from samplesneighboring the current block. For example, for directional modes,intra-prediction unit 226 may generally mathematically combine values ofneighboring samples and populate these calculated values in the defineddirection across the current block to produce the prediction block. Asanother example, for DC mode, intra-prediction unit 226 may calculate anaverage of the neighboring samples to the current block and generate theprediction block to include this resulting average for each sample ofthe prediction block.

Mode selection unit 202 provides the prediction block to residualgeneration unit 204. Residual generation unit 204 receives a raw,unencoded version of the current block from video data memory 230 andthe prediction block from mode selection unit 202. Residual generationunit 204 calculates sample-by-sample differences between the currentblock and the prediction block. The resulting sample-by-sampledifferences define a residual block for the current block. In someexamples, residual generation unit 204 may also determine differencesbetween sample values in the residual block to generate a residual blockusing residual differential pulse code modulation (RDPCM). In someexamples, residual generation unit 204 may be formed using one or moresubtractor circuits that perform binary subtraction.

In examples where mode selection unit 202 partitions CUs into PUs, eachPU may be associated with a luma prediction unit and correspondingchroma prediction units. Video encoder 200 and video decoder 300 maysupport PUs having various sizes. As indicated above, the size of a CUmay refer to the size of the luma coding block of the CU and the size ofa PU may refer to the size of a luma prediction unit of the PU. Assumingthat the size of a particular CU is 2N×2N, video encoder 200 may supportPU sizes of 2N×2N or N×N for intra prediction, and symmetric PU sizes of2N×2N, 2N×N, N×2N, N×N, or similar for inter prediction. Video encoder200 and video decoder 300 may also support asymmetric partitioning forPU sizes of 2N×nU, 2N×nD, nL×2N, and nR×2N for inter prediction.

In examples where mode selection unit 202 does not further partition aCU into PUs, each CU may be associated with a luma coding block andcorresponding chroma coding blocks. As above, the size of a CU may referto the size of the luma coding block of the CU. The video encoder 200and video decoder 300 may support CU sizes of 2N×2N, 2N×N, or N×2N.

For other video coding techniques such as an intra-block copy modecoding, an affine-mode coding, and linear model (LM) mode coding, as fewexamples, mode selection unit 202, via respective units associated withthe coding techniques, generates a prediction block for the currentblock being encoded. In some examples, such as palette mode coding, modeselection unit 202 may not generate a prediction block, and insteadgenerate syntax elements that indicate the manner in which toreconstruct the block based on a selected palette. In such modes, modeselection unit 202 may provide these syntax elements to entropy encodingunit 220 to be encoded.

As described above, residual generation unit 204 receives the video datafor the current block and the corresponding prediction block. Residualgeneration unit 204 then generates a residual block for the currentblock. To generate the residual block, residual generation unit 204calculates sample-by-sample differences between the prediction block andthe current block.

Transform processing unit 206 applies one or more transforms to theresidual block to generate a block of transform coefficients (referredto herein as a “transform coefficient block”). Transform processing unit206 may apply various transforms to a residual block to form thetransform coefficient block. For example, transform processing unit 206may apply a discrete cosine transform (DCT), a directional transform, aKarhunen-Loeve transform (KLT), or a conceptually similar transform to aresidual block. In some examples, transform processing unit 206 mayperform multiple transforms to a residual block, e.g., a primarytransform and a secondary transform, such as a rotational transform. Insome examples, transform processing unit 206 does not apply transformsto a residual block.

Quantization unit 208 may quantize the transform coefficients in atransform coefficient block, to produce a quantized transformcoefficient block. Quantization unit 208 may quantize transformcoefficients of a transform coefficient block according to aquantization parameter (QP) value associated with the current block.Video encoder 200 (e.g., via mode selection unit 202) may adjust thedegree of quantization applied to the transform coefficient blocksassociated with the current block by adjusting the QP value associatedwith the CU. Quantization may introduce loss of information, and thus,quantized transform coefficients may have lower precision than theoriginal transform coefficients produced by transform processing unit206.

Inverse quantization unit 210 and inverse transform processing unit 212may apply inverse quantization and inverse transforms to a quantizedtransform coefficient block, respectively, to reconstruct a residualblock from the transform coefficient block. Reconstruction unit 214 mayproduce a reconstructed block corresponding to the current block (albeitpotentially with some degree of distortion) based on the reconstructedresidual block and a prediction block generated by mode selection unit202. For example, reconstruction unit 214 may add samples of thereconstructed residual block to corresponding samples from theprediction block generated by mode selection unit 202 to produce thereconstructed block.

Filter unit 216 may perform one or more filter operations onreconstructed blocks. For example, filter unit 216 may performdeblocking operations to reduce blockiness artifacts along edges of CUs.Operations of filter unit 216 may be skipped, in some examples.

Video encoder 200 stores reconstructed blocks in DPB 218. For instance,in examples where operations of filter unit 216 are not needed,reconstruction unit 214 may store reconstructed blocks to DPB 218. Inexamples where operations of filter unit 216 are needed, filter unit 216may store the filtered reconstructed blocks to DPB 218. Motionestimation unit 222 and motion compensation unit 224 may retrieve areference picture from DPB 218, formed from the reconstructed (andpotentially filtered) blocks, to inter-predict blocks of subsequentlyencoded pictures. In addition, intra-prediction unit 226 may usereconstructed blocks in DPB 218 of a current picture to intra-predictother blocks in the current picture.

In general, entropy encoding unit 220 may entropy encode syntax elementsreceived from other functional components of video encoder 200. Forexample, entropy encoding unit 220 may entropy encode quantizedtransform coefficient blocks from quantization unit 208. As anotherexample, entropy encoding unit 220 may entropy encode prediction syntaxelements (e.g., motion information for inter-prediction or intra-modeinformation for intra-prediction) from mode selection unit 202. Entropyencoding unit 220 may perform one or more entropy encoding operations onthe syntax elements, which are another example of video data, togenerate entropy-encoded data. For example, entropy encoding unit 220may perform a context-adaptive variable length coding (CAVLC) operation,a CABAC operation, a variable-to-variable (V2V) length coding operation,a syntax-based context-adaptive binary arithmetic coding (SBAC)operation, a Probability Interval Partitioning Entropy (PIPE) codingoperation, an Exponential-Golomb encoding operation, or another type ofentropy encoding operation on the data. In some examples, entropyencoding unit 220 may operate in bypass mode where syntax elements arenot entropy encoded.

Video encoder 200 may output a bitstream that includes the entropyencoded syntax elements needed to reconstruct blocks of a slice orpicture. In particular, entropy encoding unit 220 may output thebitstream.

The operations described above are described with respect to a block.Such description should be understood as being operations for a lumacoding block and/or chroma coding blocks. As described above, in someexamples, the luma coding block and chroma coding blocks are luma andchroma components of a CU. In some examples, the luma coding block andthe chroma coding blocks are luma and chroma components of a PU.

In some examples, operations performed with respect to a luma codingblock need not be repeated for the chroma coding blocks. As one example,operations to identify a motion vector (MV) and reference picture for aluma coding block need not be repeated for identifying a MV andreference picture for the chroma blocks. Rather, the MV for the lumacoding block may be scaled to determine the MV for the chroma blocks,and the reference picture may be the same. As another example, theintra-prediction process may be the same for the luma coding block andthe chroma coding blocks.

Video encoder 200 represents an example of a device configured to encodevideo data including a memory configured to store video data, and one ormore processing units implemented in circuitry and configured todetermine, for each respective coding block of a plurality of codingblocks of a current coding tree unit (CTU) of video data in a currentpicture of video data, a respective search area of a plurality ofrespective search areas, wherein the search areas of the plurality ofsearch areas are all different (i.e., no two search regions encompass anidentical area, though some search regions may overlap), wherein atleast one of the plurality of search areas includes samples of thecurrent picture located outside of the current CTU, and wherein at leastone of the plurality of search areas does not include samples of thecurrent picture located outside of the current CTU; select, for eachrespective coding block and from within the respective search area forthe respective coding block, a respective predictor block of a pluralityof predictor blocks; reconstruct samples of each respective coding blockbased on samples included in a corresponding predictor block in theplurality of predictor blocks; and encode, in a video bitstream and foreach respective coding block of the plurality of coding blocks, one ormore syntax elements that represent a value of a respective vector thatidentifies the selected predictor block.

FIG. 5 is a block diagram illustrating an example video decoder 300 thatmay perform the techniques of this disclosure. FIG. 5 is provided forpurposes of explanation and is not limiting on the techniques as broadlyexemplified and described in this disclosure. For purposes ofexplanation, this disclosure describes video decoder 300 according tothe techniques of JEM, VVC, and HEVC. However, the techniques of thisdisclosure may be performed by video coding devices that are configuredto other video coding standards.

In the example of FIG. 5, video decoder 300 includes coded picturebuffer (CPB) memory 320, entropy decoding unit 302, predictionprocessing unit 304, inverse quantization unit 306, inverse transformprocessing unit 308, reconstruction unit 310, filter unit 312, anddecoded picture buffer (DPB) 314. Any or all of CPB memory 320, entropydecoding unit 302, prediction processing unit 304, inverse quantizationunit 306, inverse transform processing unit 308, reconstruction unit310, filter unit 312, and DPB 314 may be implemented in one or moreprocessors or in processing circuitry. For instance, the units of videodecoder 300 may be implemented as one or more circuits or logic elementsas part of hardware circuitry, or as part of a processor, ASIC, of FPGA.Moreover, video decoder 300 may include additional or alternativeprocessors or processing circuitry to perform these and other functions.

Prediction processing unit 304 includes motion compensation unit 316 andintra-prediction unit 318. Prediction processing unit 304 may includeadditional units to perform prediction in accordance with otherprediction modes. As examples, prediction processing unit 304 mayinclude a palette unit, an intra-block copy unit (which may form part ofmotion compensation unit 316), an affine unit, a linear model (LM) unit,or the like. In other examples, video decoder 300 may include more,fewer, or different functional components.

CPB memory 320 may store video data, such as an encoded video bitstream,to be decoded by the components of video decoder 300. The video datastored in CPB memory 320 may be obtained, for example, fromcomputer-readable medium 110 (FIG. 1). CPB memory 320 may include a CPBthat stores encoded video data (e.g., syntax elements) from an encodedvideo bitstream. Also, CPB memory 320 may store video data other thansyntax elements of a coded picture, such as temporary data representingoutputs from the various units of video decoder 300. DPB 314 generallystores decoded pictures, which video decoder 300 may output and/or useas reference video data when decoding subsequent data or pictures of theencoded video bitstream. CPB memory 320 and DPB 314 may be formed by anyof a variety of memory devices, such as DRAM, including SDRAM, MRAM,RRAM, or other types of memory devices. CPB memory 320 and DPB 314 maybe provided by the same memory device or separate memory devices. Invarious examples, CPB memory 320 may be on-chip with other components ofvideo decoder 300, or off-chip relative to those components.

Additionally or alternatively, in some examples, video decoder 300 mayretrieve coded video data from memory 120 (FIG. 1). That is, memory 120may store data as discussed above with CPB memory 320. Likewise, memory120 may store instructions to be executed by video decoder 300, whensome or all of the functionality of video decoder 300 is implemented insoftware to be executed by processing circuitry of video decoder 300.

The various units shown in FIG. 5 are illustrated to assist withunderstanding the operations performed by video decoder 300. The unitsmay be implemented as fixed-function circuits, programmable circuits, ora combination thereof. Similar to FIG. 3, fixed-function circuits referto circuits that provide particular functionality, and are preset on theoperations that can be performed. Programmable circuits refer tocircuits that can be programmed to perform various tasks, and provideflexible functionality in the operations that can be performed. Forinstance, programmable circuits may execute software or firmware thatcause the programmable circuits to operate in the manner defined byinstructions of the software or firmware. Fixed-function circuits mayexecute software instructions (e.g., to receive parameters or outputparameters), but the types of operations that the fixed-functioncircuits perform are generally immutable. In some examples, one or moreof the units may be distinct circuit blocks (fixed-function orprogrammable), and in some examples, one or more of the units may beintegrated circuits.

Video decoder 300 may include ALUs, EFUs, digital circuits, analogcircuits, and/or programmable cores formed from programmable circuits.In examples where the operations of video decoder 300 are performed bysoftware executing on the programmable circuits, on-chip or off-chipmemory may store instructions (e.g., object code) of the software thatvideo decoder 300 receives and executes.

Entropy decoding unit 302 may receive encoded video data from the CPBand entropy decode the video data to reproduce syntax elements.Prediction processing unit 304, inverse quantization unit 306, inversetransform processing unit 308, reconstruction unit 310, and filter unit312 may generate decoded video data based on the syntax elementsextracted from the bitstream.

In general, video decoder 300 reconstructs a picture on a block-by-blockbasis. Video decoder 300 may perform a reconstruction operation on eachblock individually (where the block currently being reconstructed, i.e.,decoded, may be referred to as a “current block”).

Entropy decoding unit 302 may entropy decode syntax elements definingquantized transform coefficients of a quantized transform coefficientblock, as well as transform information, such as a quantizationparameter (QP) and/or transform mode indication(s). Inverse quantizationunit 306 may use the QP associated with the quantized transformcoefficient block to determine a degree of quantization and, likewise, adegree of inverse quantization for inverse quantization unit 306 toapply. Inverse quantization unit 306 may, for example, perform a bitwiseleft-shift operation to inverse quantize the quantized transformcoefficients. Inverse quantization unit 306 may thereby form a transformcoefficient block including transform coefficients.

After inverse quantization unit 306 forms the transform coefficientblock, inverse transform processing unit 308 may apply one or moreinverse transforms to the transform coefficient block to generate aresidual block associated with the current block. For example, inversetransform processing unit 308 may apply an inverse DCT, an inverseinteger transform, an inverse Karhunen-Loeve transform (KLT), an inverserotational transform, an inverse directional transform, or anotherinverse transform to the transform coefficient block.

Furthermore, prediction processing unit 304 generates a prediction blockaccording to prediction information syntax elements that were entropydecoded by entropy decoding unit 302. For example, if the predictioninformation syntax elements indicate that the current block isinter-predicted, motion compensation unit 316 may generate theprediction block. In this case, the prediction information syntaxelements may indicate a reference picture in DPB 314 from which toretrieve a reference block, as well as a motion vector identifying alocation of the reference block in the reference picture relative to thelocation of the current block in the current picture. Motioncompensation unit 316 may generally perform the inter-prediction processin a manner that is substantially similar to that described with respectto motion compensation unit 224 (FIG. 4).

As another example, if the prediction information syntax elementsindicate that the current block is intra-predicted, intra-predictionunit 318 may generate the prediction block according to anintra-prediction mode indicated by the prediction information syntaxelements. Again, intra-prediction unit 318 may generally perform theintra-prediction process in a manner that is substantially similar tothat described with respect to intra-prediction unit 226 (FIG. 4).Intra-prediction unit 318 may retrieve data of neighboring samples tothe current block from DPB 314.

Reconstruction unit 310 may reconstruct the current block using theprediction block and the residual block. For example, reconstructionunit 310 may add samples of the residual block to corresponding samplesof the prediction block to reconstruct the current block.

Filter unit 312 may perform one or more filter operations onreconstructed blocks. For example, filter unit 312 may performdeblocking operations to reduce blockiness artifacts along edges of thereconstructed blocks. Operations of filter unit 312 are not necessarilyperformed in all examples.

Video decoder 300 may store the reconstructed blocks in DPB 314. Forinstance, in examples where operations of filter unit 312 are notperformed, reconstruction unit 310 may store reconstructed blocks to DPB314. In examples where operations of filter unit 312 are performed,filter unit 312 may store the filtered reconstructed blocks to DPB 314.As discussed above, DPB 314 may provide reference information, such assamples of a current picture for intra-prediction and previously decodedpictures for subsequent motion compensation, to prediction processingunit 304. Moreover, video decoder 300 may output decoded pictures (e.g.,decoded video) from DPB 314 for subsequent presentation on a displaydevice, such as display device 118 of FIG. 1.

In this manner, video decoder 300 represents an example of a videodecoding device including a memory configured to store video data, andone or more processing units implemented in circuitry and configured todetermine, for each respective coding block of a plurality of codingblocks of a current coding tree unit (CTU) of video data in a currentpicture of video data, a respective search area of a plurality ofrespective search areas, wherein the search areas of the plurality ofsearch areas are all different, wherein at least one of the plurality ofsearch areas includes samples of the current picture located outside ofthe current CTU, and wherein at least one of the plurality of searchareas does not include samples of the current picture located outside ofthe current CTU; decode, from a video bitstream and for each respectivecoding block of the plurality of coding blocks, one or more syntaxelements that represent a value of a vector that identifies a predictorblock in the respective search area; select, for each respective codingblock and based on the respective vector, the respective predictor blockof a plurality of predictor blocks; and reconstruct samples of eachrespective coding block based on samples included in a correspondingpredictor block in the plurality of predictor blocks.

FIG. 6 is a conceptual diagram illustrating a coding tree unit (CTU)coded using a pipeline, in accordance with one or more techniques ofthis disclosure. As shown in FIG. 6, CTU 600 may be split into virtualpipeline data units (VPDUs) 602A-602D (collectively, “VPDUs 602”). Forinstance, where CTU 600 include 128×128 samples, CTU 600 may be splitinto VPDUs 602, each of which may include 64×64 samples. In someimplementations of CPR, video coders (e.g., video encoder 200 and/orvideo decoder 300) may utilize pipelines configured to process codingunits of 64×64 samples.

As discussed above, this disclosure describes techniques in which avideo coder may include samples from outside of a current CTU in searchareas used when predicting coding blocks of the current CTU using CPR(e.g., CPR search areas). This disclosure describes several techniquesfor extending the CPR search areas, each of which may be usedindependently or in combination with any other technique.

In accordance with a first technique of this disclosure, a video codermay include A rows above the current CTU and B columns to the left ofthe current CTU in the CPR search area. The available number of lines Aand B may depend on pixels used by other tools such as intra predictionand deblocking filter. Including these samples may not significantlyincrease the memory requirements as the samples around a CTU may alreadybe used for intra prediction and deblocking filtering.

In accordance with a second technique of this disclosure, a video codermay use different search areas for different coding blocks in thecurrent CTU. For instance, the video coder may selectively include Arows above the current CTU and B columns to the left of the current CTU(e.g., the search area of the first technique) in the CPR search areaused for some coding blocks but not others. As one example, the videocoder may selectively include A rows above the current CTU and B columnsto the left of the current CTU in the CPR search area uses for codingblocks located at the left and/or above borders of the current CTU.

FIG. 7 is a conceptual diagram illustrating example search areas usedfor CPR, in accordance with one or more techniques of this disclosure.As shown in FIG. 7, CTU 700 may divided into M×N coding blocks702(0,0)-702(M−1,N−1). As discussed above, a video coder may usedifferent search areas for different coding blocks in the current CTU.The search area used for a particular coding block of a CTU may bedetermined based on the location of the particular coding block withinthe CTU. As one example, the video coder may include samples from Aabove lines from above-neighboring CTUs 704 and top-left neighboring CTU708 in search areas for coding blocks located in a topmost row of CTU700 (i.e., coding blocks in row n=0). As another example, the videocoder may include samples from B left columns from left-neighboring CTUs706 and top-left neighboring CTU 708 in search areas for coding blockslocated in a leftmost column of CTU 700 (i.e., coding blocks in columnm=0). As such, the search area for coding block 702(0,0) may includeboth A above lines from above-neighboring CTUs 704 and top-leftneighboring CTU 708 along with B left columns from left-neighboring CTUs706 and top-left neighboring CTU 708.

FIG. 8 is a conceptual diagram illustrating example search areas usedfor CPR, in accordance with one or more techniques of this disclosure.As shown in FIG. 8, CTU 800 may divided into four coding blocks802A-802D (collectively, “coding blocks 802”). In some examples, codingblocks 802 may be referred to as VPDUs. For instance, where CTU 800include 128×128 samples, CTU 800 may be split into VPDUs 802, each ofwhich may include 64×64 samples.

Coding blocks 802 may be referred to based on their relative positionwithin CTU 800. As one example, coding block 802A may be referred to asa top-left coding block. As another example, coding block 802B may bereferred to as a top-right coding block. As another example, codingblock 802C may be referred to as a bottom-left coding block. As anotherexample, coding block 802D may be referred to as a bottom-right codingblock.

CTU 800 may be located in a picture of video data along with other CTUs.The other CTUs may be located in areas that are referred to based ontheir relative position to CTU 800. As one example, top-neighboring area804 may include one or more CTUs located above CTU 800. As anotherexample, left-neighboring area 806 may include one or more CTUs locatedto the left of CTU 800. As another example, top-left-neighboring area808 may include a CTU located to the top-left of CTU 800.

As discussed above, a video coder may utilize hybrid search areas forcoding blocks of a CTU. For instance, the video coder may utilize adifferent search area for each of coding block 802. The search areas maybe considered hybrid in that the search area for at least one codingblock of coding blocks 802 includes samples of the current picturelocated outside of CTU 800, and the search area for at least one codingblock of coding blocks 802 does not include samples of the currentpicture located outside of CTU 800.

The video coder may determine a respective search area for each codingblock of coding blocks 802. In the example of FIG. 8, the video codermay determine that the search area for coding block 802A includes atleast some samples located outside of CTU 800. For instance, the videocoder may include up to N top line(s) above CTU 800 (e.g., up to N rowsfrom above-neighboring area 804), up to M left column(s) of CTU 800(e.g., up to M columns from left-neighboring area 806), and/or top-leftneighboring area 808 in the search area for coding block 802A. As such,in some examples, the search area for coding block 802A may includesamples from a coding block in a CTU located to the left of coding block802A of CTU 800.

The video coder may determine that the search area for coding block 802Bincludes at least some samples located outside of CTU 800 and at leastsome samples located inside CTU 800. For instance, the video coder mayinclude up to N top line(s) above CTU 800 (e.g., up to N rows fromabove-neighboring area 804) and/or samples from coding block 802A in thesearch area for coding block 802B.

The video coder may determine that the search area for coding block 802Cincludes at least some samples located outside of CTU 800 and at leastsome samples located inside CTU 800. For instance, the video coder mayinclude up to M left column(s) of CTU 800 (e.g., up to M columns fromleft-neighboring area 806), samples from coding block 802A, and/orsamples from coding block 802B in the search area for coding block 802B.

The video coder may determine that the search area for coding block 802Cdoes not include samples located outside CTU 800. For instance, thevideo coder may include up samples from coding block 802A, samples fromcoding block 802B, and/or samples from coding block 802C in the searcharea for coding block 802B. However, the video coder may not includesamples from left-neighboring area 806 in the search area for codingblock 802B.

In view of the above, in some examples, the video coder may determinethat the the respective search areas for the top-left coding block, thetop-right coding block, and the bottom-left coding block include samplesof the current picture located outside of the current CTU. For instance,the video coder may determine that the search areas for each of codingblocks 802A, 802B, and 802C include samples located outside of CTU 800.Similarly, the video coder may determine that the respective searchareas for the top-left coding block and the bottom-left coding blockinclude samples of the current picture located in a left-neighboring CTUof the current CTU. For instance, the video coder may determine that thesearch areas for each of coding blocks 802A and 802C include sampleslocated in a CTU of left-neighboring area 806.

Additionally, in some examples, the video coder may determine that therespective search area for the bottom-right coding block does notinclude samples of the current picture located outside of the currentCTU. For instance, the video coder may determine that the search areacoding block 802D does not include samples located outside of CTU 800.Similarly, the video coder may determine that the respective search areafor the bottom-right coding block includes the top-left coding block,the top-right coding block, and the bottom-left coding block. Forinstance, the video coder may determine that the search area for codingblock 802D includes samples from coding blocks 802A, 802B, and 802C.

In accordance with a third technique of this disclosure, a video codermay code a current VPDU of a current CTU using CPR with a search areathat includes previously coded VPDUs within the current CTU and theencoded area within the current VPDU. Which VPDUs are consideredpreviously coded VPDUs may be a function of coding order.

FIGS. 9A-9C are conceptual diagrams illustrating example search areasused for performing CPR with various scan orders, in accordance with oneor more techniques of this disclosure. Each of FIGS. 9A-9C illustratescurrent CTU 900 divided into M×N VPDUs 902(0,0)-902(M−1,N−1)(collectively, “VPDUs 902”). For purposes of explanation, VPDU 902(1,1)will be used as the current VPDU. As shown in FIGS. 902A-902C, VPDU902(1,1) may be divided into blocks 904A-904D (collectively, “blocks904”). In each of FIGS. 9A-9C, the video coder may include the shadedVPDUs of VPDUs 902 in the search area used for VPDU 902(1,1) (i.e., thecurrent VPDU).

FIG. 9A, illustrates an example search areas used for performing CPRwith horizontal raster scan order (e.g., left to right, top to bottom).As shown in FIG. 9A, the video coder may include the VPDUs in the VPDUlines above the current VPDU, and the VPDUs to the left of the currentVPDU at the same VPDU line in the search area for the current VPDU. Insome examples, the video coder may include blocks within the currentVPDU in the search area for other blocks within the current VPDU. Forinstance, the video coder may include blocks 904A, 904B, and 904C in thesearch area for block 904D. In some examples, the video coder mayinclude VPDUs of VPDUs 902 shown in white color (unshaded), whichcontain samples from a previously processed CTU (e.g., the CTUimmediately preceding CTU 900 in coding order) in the search area forblocks of CTU 900.

FIG. 9B, illustrates an example search areas used for performing CPRwith vertical raster scan order (e.g., top to bottom, left to right). Asshown in FIG. 9B, the video coder may include the VPDUs in the VPDUcolumns to the left of the current VPDU, and the VPDUs above the currentVPDU at the same VPDU column in the search area for the current VPDU. Insome examples, the video coder may include blocks within the currentVPDU in the search area for other blocks within the current VPDU. Forinstance, the video coder may include blocks 904A, 904B, and 904C in thesearch area for block 904D. In some examples, the video coder mayinclude VPDUs of VPDUs 902 shown in white color (unshaded), whichcontain samples from a previously processed CTU (e.g., the CTUimmediately preceding CTU 900 in coding order) in the search area forblocks of CTU 900.

FIG. 9C, illustrates an example search areas used for performing CPRwith zig-zag scan order. As shown in FIG. 9C, the video coder mayinclude the VPDUs to the left of the current VPDU in the zig-zag orderin the search area for the current VPDU. In some examples, the videocoder may include blocks within the current VPDU in the search area forother blocks within the current VPDU. For instance, the video coder mayinclude blocks 904A, 904B, and 904C in the search area for block 904D.In some examples, the video coder may include VPDUs of VPDUs 902 shownin white color (unshaded), which contain samples from a previouslyprocessed CTU (e.g., the CTU immediately preceding CTU 900 in codingorder) in the search area for blocks of CTU 900.

FIG. 10 is a conceptual diagram illustrating example search areas usedfor CPR, in accordance with one or more techniques of this disclosure.As shown in FIG. 10, CTU 1000 may divided into four coding blocks1002A-1002D (collectively, “coding blocks 1002”). In some examples,coding blocks 1002 may be referred to as VPDUs. For instance, where CTU1000 include 128×128 samples, CTU 1000 may be split into VPDUs 1002,each of which may include 64×64 samples.

As discussed above, a video coder may include samples from previouslycoded VPDUs of a current CTU in a search area for a current VPDU of thecurrent CTU (e.g., for performing CPR). As shown in FIG. 10, the codingorder may be VPDU 1002A-1002B-1002C-1002D. In this example, the videocoder may include VPDU 1002A in the search area for VPDU 1002B (e.g.,VPDU 1002B may use VPDU 1002A for reference). The video coder mayinclude VPDU 1002A and VPDU 1002B in the search area for VPDU 1002C. Thevideo coder may include VPDUs 1002A-1002C in the search area for VPDU1002D.

FIG. 11 is a conceptual diagram illustrating example search areas usedfor CPR, in accordance with one or more techniques of this disclosure.As shown in FIG. 11, CTU 1100 may divided into four coding blocks1102A-1102D (collectively, “coding blocks 1102”). In some examples,coding blocks 1102 may be referred to as VPDUs. For instance, where CTU1100 include 128×128 samples, CTU 1100 may be split into VPDUs 1102,each of which may include 64×64 samples.

As discussed above, a video coder may include samples from previouslycoded VPDUs of a current CTU in a search area for a current VPDU of thecurrent CTU (e.g., for performing CPR). As shown in FIG. 11, the codingorder may be VPDU 1102A-1102C-1102B-1102D. In this example, the videocoder may include VPDU 1102A in the search area for VPDU 1102C (e.g.,VPDU 1102C may use VPDU 1102A for reference). The video coder mayinclude VPDU 1102A and VPDU 1102C in the search area for VPDU 1102B. Thevideo coder may include VPDUs 1102A-1102C in the search area for VPDU1102D.

In accordance with a fourth technique of this disclosure, a video codermay include a combination of samples from neighboring CTUs and samplesfrom other coding blocks in a current CTU in a search area for a codingblock in the current CTU. For instance, the CPR search area of a VPDUmay includes the neighbour samples and the reconstructed area within thecurrent VPDU. The configuration and/or definition of theavailable-for-CPR reference area, which may comprise the neighboursamples and the size of the reference area, may depend on the positionof the VPDU within a CTU.

FIGS. 12A-12D are conceptual diagrams illustrating example search areasused for performing CPR for various coding blocks of a CTU, inaccordance with one or more techniques of this disclosure. Each of FIGS.12A-12D illustrates current CTU 1200 divided into four coding blocks1202A-1202D (collectively, “coding blocks 1202”). In some examples,coding blocks 1202 may be referred to as VPDUs. For instance, where CTU1200 include 128×128 samples, CTU 1200 may be split into VPDUs 1202,each of which may include 64×64 samples. The shaded region in each ofFIGS. 12A-12D may represent the search area uses for a current block. Ineach of FIGS. 12A-12D, the shaded region (and thus the search area) mayinclude above lines 1204 (e.g., n above lines) and left columns 1206(e.g., m left columns). The position of above lines 1204 and leftcolumns 1206 may change based on the position of the current block.

FIG. 12A illustrates an example search area for coding block 1202A, alsoreferred to as a top-left coding block. As shown in FIG. 12A, abovelines 1204 and left columns 1206 may both be located outside of CTU1200.

FIG. 12B illustrates an example search area for coding block 1202A, alsoreferred to as a top-right coding block. As shown in FIG. 12B, abovelines 1204 may be located outside of CTU 1200, while left columns 1206may be at least partially located within CTU 1200.

FIG. 12C illustrates an example search area for coding block 1202A, alsoreferred to as a bottom-left coding block. As shown in FIG. 12C, leftcolumns 1206 may be located outside of CTU 1200, while above lines 1204may be at least partially located within CTU 1200.

FIG. 12D illustrates an example search area for coding block 1202A, alsoreferred to as a bottom-right coding block. As shown in FIG. 12D, abovelines 1204 and left columns 1206 may both be located within of CTU 1200.

In one example, M, N, m, and n lines can be in the range from 1 to 4inclusive. As mentioned earlier, in another example, M, N, m, and n canbe determined by the number of lines required for other tools, such asintra prediction and deblocking filter.

In another example, M and N lines located outside of a CTU may havedifferent count from m and n lines located inside the CTU. For example,M and N can be equal to 1, while m and n may be equal to 4.

In various examples, the techniques above can be applied to other CTUand VPDU sizes. For example, CTU size can be 256. In another example,VPDU size can be 32×32. Other VPDU and CTU sizes may also be utilized incombination with the above techniques.

FIG. 13 is a flowchart illustrating an example method for encoding acurrent block. The current block may comprise a current CU. Althoughdescribed with respect to video encoder 200 (FIGS. 1 and 4), it shouldbe understood that other devices may be configured to perform a methodsimilar to that of FIG. 13.

In this example, video encoder 200 initially predicts the current block(350). For example, video encoder 200 may form a prediction block forthe current block. For instance, where the current block is a currentcoding block of a plurality of coding blocks of a current coding treeunit (CTU), video encoder 200 may determine, for each respective codingblock of the plurality of coding blocks, a respective search area of aplurality of respective search areas. In some examples, the search areasof the plurality of search areas may all be different. In some examples,at least one of the plurality of search areas includes samples of thecurrent picture located outside of the current CTU. In some examples, atleast one of the plurality of search areas does not include samples ofthe current picture located outside of the current CTU.

Video encoder 200 may then calculate a residual block for the currentblock (352). To calculate the residual block, video encoder 200 maycalculate a difference between the original, unencoded block and theprediction block for the current block. Video encoder 200 may thentransform and quantize coefficients of the residual block (354). Next,video encoder 200 may scan the quantized transform coefficients of theresidual block (356). During the scan, or following the scan, videoencoder 200 may entropy encode the transform coefficients (358). Forexample, video encoder 200 may encode the transform coefficients usingCAVLC or CABAC. Video encoder 200 may then output the entropy encodeddata of the block (360).

FIG. 14 is a flowchart illustrating an example method for decoding acurrent block of video data. The current block may comprise a currentCU. Although described with respect to video decoder 300 (FIGS. 1 and5), it should be understood that other devices may be configured toperform a method similar to that of FIG. 14.

Video decoder 300 may receive entropy encoded data for the currentblock, such as entropy encoded prediction information and entropyencoded data for coefficients of a residual block corresponding to thecurrent block (370). Video decoder 300 may entropy decode the entropyencoded data to determine prediction information for the current blockand to reproduce coefficients of the residual block (372). Video decoder300 may predict the current block (374), e.g., using an intra- orinter-prediction mode as indicated by the prediction information for thecurrent block, to calculate a prediction block for the current block.For instance, where the current block is a current coding block of aplurality of coding blocks of a current coding tree unit (CTU), videodecoder 300 may determine, for each respective coding block of theplurality of coding blocks, a respective search area of a plurality ofrespective search areas. In some examples, the search areas of theplurality of search areas may all be different. In some examples, atleast one of the plurality of search areas includes samples of thecurrent picture located outside of the current CTU. In some examples, atleast one of the plurality of search areas does not include samples ofthe current picture located outside of the current CTU.

Video decoder 300 may then inverse scan the reproduced coefficients(376), to create a block of quantized transform coefficients. Videodecoder 300 may then inverse quantize and inverse transform thetransform coefficients to produce a residual block (378). Video decoder300 may ultimately decode the current block by combining the predictionblock and the residual block (380).

FIG. 15 is a flowchart illustrating an example method for predicting ablock of video data in a current picture using hybrid search areas, inaccordance with the techniques of this disclosure. The current block maycomprise a current coding block of a current coding tree unit (CTU).Although described with respect to video encoder 200 (FIGS. 1 and 4), itshould be understood that other devices may be configured to perform amethod similar to that of FIG. 15. For instance, video decoder 300(FIGS. 1 and 5) may be configured to perform a method similar to that ofFIG. 15.

Video encoder 200 may determine a respective search area for each codingblock of a plurality of coding blocks of a current CTU of a currentpicture (1502). For instance, video encoder 200 may determine adifferent search area for each of coding blocks 802 of FIG. 8. Thevarious search areas may be considered hybrid search areas in that someinclude samples located outside of the current CTU and some do notinclude samples located outside of the current CTU.

At least one of the plurality of search areas may include at least somesamples of the current picture located outside of the current CTU. Forinstance, the respective search areas for coding block 802A (e.g., thetop-left coding block), coding block 802B (e.g., the top-right codingblock), and coding block 802C (e.g., the bottom-left coding block) mayinclude samples of the current picture located outside of CTU 800. Asone example, the respective search areas for the top-left coding blockand the bottom-left coding block may include samples of the currentpicture located in a left-neighboring CTU of the current CTU.

At least one of the plurality of search areas may not include samples ofthe current picture located outside of the current CTU. For instance,the respective search area for coding block 802D (e.g., the bottom-rightcoding block) may not include samples of the current picture locatedoutside of CTU 800. As one example, the respective search area for thebottom-right coding block may include the top-left coding block, thetop-right coding block, and the bottom-left coding block.

Video encoder 200 may select a respective predictor block for eachcoding block from within the respective search area of the coding block(1504). For instance, video encoder 200 may select a block from withinthe search area for coding block 802A that includes samples that mostclosely match samples of coding block 802A (e.g., that would yield thesmallest residual values), select a block from within the search areafor coding block 802B that includes samples that most closely matchsamples of coding block 802B, select a block from within the search areafor coding block 802C that includes samples that most closely matchsamples of coding block 802C, and select a block from within the searcharea for coding block 802D that includes samples that most closely matchsamples of coding block 802D.

Video encoder 200 may determine a respective vector for each codingblock, each respective vector identifying the respective predictor blockfor the respective coding block. For instance, video encoder 200 maydetermine a motion vector (also referred to as a block vector) thatrepresents a displacement between coding block 802A and the predictorblock for coding block 802A. The motion vector may have a horizontalcomponent that represents a horizontal displacement between the codingblock 802A and the predictor block for coding block 802A and a verticalcomponent that represents a vertical displacement between coding block802A and the predictor block for coding block 802A.

Video encoder 200 may encode, in a coded video bitstream, arepresentation of the vector. For instance, motion compensation unit 224may select a motion vector predictor (MVP) and subtract the determinedmotion vector from the MVP to determine a motion vector difference(MVD). Motion compensation unit 224 may cause entropy encoding unit 220to encode, in the coded video bitstream, one or more syntax elementsthat represent a value of the MVD. Video encoder 200 may similarlydetermine and encode a motion vector for each of coding blocks802B-802D).

Video encoder 200 may reconstruct samples of each coding block (1506).For instance, as part of a reconstruction loop, video encoder 200 mayadd samples of the selected predictor block for coding block 802A toresidual data to reconstruct the values of coding block 802A. Videoencoder 200 may similarly reconstruct the samples of coding blocks802B-802D (e.g., based on their respective predictor blocks andrespective residual data).

It is to be recognized that depending on the example, certain acts orevents of any of the techniques described herein can be performed in adifferent sequence, may be added, merged, or left out altogether (e.g.,not all described acts or events are necessary for the practice of thetechniques). Moreover, in certain examples, acts or events may beperformed concurrently, e.g., through multi-threaded processing,interrupt processing, or multiple processors, rather than sequentially.

In one or more examples, the functions described may be implemented inhardware, software, firmware, or any combination thereof. If implementedin software, the functions may be stored on or transmitted over as oneor more instructions or code on a computer-readable medium and executedby a hardware-based processing unit. Computer-readable media may includecomputer-readable storage media, which corresponds to a tangible mediumsuch as data storage media, or communication media including any mediumthat facilitates transfer of a computer program from one place toanother, e.g., according to a communication protocol. In this manner,computer-readable media generally may correspond to (1) tangiblecomputer-readable storage media which is non-transitory or (2) acommunication medium such as a signal or carrier wave. Data storagemedia may be any available media that can be accessed by one or morecomputers or one or more processors to retrieve instructions, codeand/or data structures for implementation of the techniques described inthis disclosure. A computer program product may include acomputer-readable medium.

By way of example, and not limitation, such computer-readable storagemedia can comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage, or other magnetic storage devices, flashmemory, or any other medium that can be used to store desired programcode in the form of instructions or data structures and that can beaccessed by a computer. Also, any connection is properly termed acomputer-readable medium. For example, if instructions are transmittedfrom a website, server, or other remote source using a coaxial cable,fiber optic cable, twisted pair, digital subscriber line (DSL), orwireless technologies such as infrared, radio, and microwave, then thecoaxial cable, fiber optic cable, twisted pair, DSL, or wirelesstechnologies such as infrared, radio, and microwave are included in thedefinition of medium. It should be understood, however, thatcomputer-readable storage media and data storage media do not includeconnections, carrier waves, signals, or other transitory media, but areinstead directed to non-transitory, tangible storage media. Disk anddisc, as used herein, includes compact disc (CD), laser disc, opticaldisc, digital versatile disc (DVD), floppy disk and Blu-ray disc, wheredisks usually reproduce data magnetically, while discs reproduce dataoptically with lasers. Combinations of the above should also be includedwithin the scope of computer-readable media.

Instructions may be executed by one or more processors, such as one ormore digital signal processors (DSPs), general purpose microprocessors,application specific integrated circuits (ASICs), field programmablegate arrays (FPGAs), or other equivalent integrated or discrete logiccircuitry. Accordingly, the term “processor,” as used herein may referto any of the foregoing structure or any other structure suitable forimplementation of the techniques described herein. In addition, in someaspects, the functionality described herein may be provided withindedicated hardware and/or software modules configured for encoding anddecoding, or incorporated in a combined codec. Also, the techniquescould be fully implemented in one or more circuits or logic elements.

The techniques of this disclosure may be implemented in a wide varietyof devices or apparatuses, including a wireless handset, an integratedcircuit (IC) or a set of ICs (e.g., a chip set). Various components,modules, or units are described in this disclosure to emphasizefunctional aspects of devices configured to perform the disclosedtechniques, but do not necessarily require realization by differenthardware units. Rather, as described above, various units may becombined in a codec hardware unit or provided by a collection ofinteroperative hardware units, including one or more processors asdescribed above, in conjunction with suitable software and/or firmware.

Various examples have been described. These and other examples arewithin the scope of the following claims.

What is claimed is:
 1. A method of coding video data, the methodcomprising: determining, for each respective coding block of a pluralityof coding blocks of a current unit of video data in a current picture ofthe video data, a respective search area of a plurality of respectivesearch areas, wherein the search areas of the plurality of search areasare all different, wherein the respective search area for a particularcoding block includes M left columns of the particular coding block;selecting, for each respective coding block and from within therespective search area for the respective coding block, a respectivepredictor block of a plurality of predictor blocks; and reconstructingsamples of each respective coding block based on samples included in acorresponding predictor block in the plurality of predictor blocks. 2.The method of claim 1, further comprising: selectively determining,based on a coding characteristic of the particular coding block, a valueof M for the particular coding block.
 3. The method of claim 2, whereinthe coding characteristic comprises a number of lines used by othertools.
 4. The method of claim 1, wherein a value of M is in a range of 1to 4, inclusive.
 5. The method of claim 1, wherein the respective searcharea for the particular coding block includes N above lines of theparticular coding block.
 6. The method of claim 5, wherein a value of Nis in a range of 1 to 4, inclusive.
 7. The method of claim 1, whereineach of the coding blocks comprises a 64×64 sample block of video data.8. The method of claim 1, further comprising: decoding, from a videobitstream and for each respective coding block of the plurality ofcoding blocks, one or more syntax elements that represent a value of avector that identifies the selected predictor block, wherein selectingthe predictor block for a respective coding block comprises selectingthe predictor block based on the value of the vector.
 9. The method ofclaim 1, further comprising: encoding, in a video bitstream and for eachrespective coding block of the plurality of coding blocks, one or moresyntax elements that represent a value of a respective vector thatidentifies the selected predictor block.
 10. A device for coding videodata, the device comprising: a memory configured to store the videodata; and one or more processors implemented in circuitry and configuredto: determine, for each respective coding block of a plurality of codingblocks of a current coding tree unit (CTU) of the video data in acurrent picture of video data, a respective search area of a pluralityof respective search areas, wherein the search areas of the plurality ofsearch areas are all different, wherein the respective search area for aparticular coding block includes M left columns of the particular codingblock; select, for each respective coding block and from within therespective search area for the respective coding block, a respectivepredictor block of a plurality of predictor blocks; and reconstructsamples of each respective coding block based on samples included in acorresponding predictor block in the plurality of predictor blocks. 11.The device of claim 10, wherein the one or more processors areconfigured to: selectively determine, based on a coding characteristicof the particular coding block, a value of M for the particular codingblock.
 12. The device of claim 11, wherein the coding characteristiccomprises a number of lines used by other tools.
 13. The device of claim10, wherein a value of M is in a range of 1 to 4, inclusive.
 14. Thedevice of claim 10, wherein the respective search area for theparticular coding block includes N above lines of the particular codingblock.
 15. The device of claim 14, wherein a value of N is in a range of1 to 4, inclusive.
 16. The device of claim 10, wherein each of thecoding blocks comprises a 64×64 sample block of video data.
 17. Thedevice of claim 10, wherein the one or more processors are furtherconfigured to: decode, from a video bitstream and for each respectivecoding block of the plurality of coding blocks, one or more syntaxelements that represent a value of a vector that identifies the selectedpredictor block, wherein, to select the predictor block for a respectivecoding block, the one or more processors are configured to select thepredictor block based on the value of the vector.
 18. Acomputer-readable storage medium having stored thereon instructionsthat, when executed, cause one or more processors to: determine, foreach respective coding block of a plurality of coding blocks of acurrent coding tree unit (CTU) of video data in a current picture ofvideo data, a respective search area of a plurality of respective searchareas, wherein the search areas of the plurality of search areas are alldifferent, wherein the respective search area for a particular codingblock includes M left columns of the particular coding block; select,for each respective coding block and from within the respective searcharea for the respective coding block, a respective predictor block of aplurality of predictor blocks; and reconstruct samples of eachrespective coding block based on samples included in a correspondingpredictor block in the plurality of predictor blocks.
 19. Thecomputer-readable storage medium of claim 18, further comprisinginstructions that cause the one or more processors to: selectivelydetermine, based on a coding characteristic of the particular codingblock, a value of M for the particular coding block.
 20. Thecomputer-readable storage medium of claim 18, wherein the respectivesearch area for the particular coding block includes N above lines ofthe particular coding block, and wherein M is different than N.